Method And Device For Automatically Estimating An Air Speed Of An Aircraft

ABSTRACT

The device ( 1 ) comprises means for registering, in case of detection of a ground taxiing of the aircraft, the last value of static pressure corrected from induced aerodynamic effects.

The present invention relates to a process and a device for automatically estimating an air speed of an airplane, in particular of a transport airplane. It also relates to a method and a system for automatically managing the activation of thrust reversers of an airplane, comprising respectively such a process and such a device.

It is known that, on-board an airplane, it is important to know some information about the flight of the airplane. Anemometric measurement techniques enable to know such information, and more specifically, the speed of the airplane, its position in the space with respect to the air, its altitude as well as direct air parameters. Such parameters, referred to as anemoclinometric parameters, essentially include:

-   -   the total pressure;     -   the static pressure;     -   the leading angle representing the angle between the chord of a         wing of the airplane and the direction of the air flow wherein         the airplane is moving;     -   the sideslip angle representing the angle of the air flow with         respect to the trajectory of the airplane; and     -   the total air temperature TAT.

In order to have access to such anemoclinometric parameters, current airplanes use usual measurement instruments, using properties relating to the dynamics of the surrounding air, i.e. generally:

-   -   total pressure probes (Pitot tubes);     -   static pressure probes for measuring the atmospheric pressure;     -   paddles or weathercocks for determining the leading and the         sideslip angles; and     -   total temperature probes.

Such measurement instruments, including such probes, are directly connected to circuitry or to computers in the airplane. More particularly, the navigation systems of the airplane generally comprise one or more primary circuitry of the ADIRU (<<Air Data Reference Inertial Unit>>) type, and one or optionally more standby circuitry. Said primary circuitry each comprise means for processing rough data, supplied by said probes, for deducing therefrom the anemoclinometric parameters required for a good operation of the airplane. Moreover, said standby circuit is used should primary circuitry fail (with the aim at overcoming such a failure) or for clearing up a doubt about the accuracy of primary parameters.

Furthermore, it is known that the engines of an airplane are generally provided with thrust reversers. A thrust reverser is a device allowing to direct forward the thrust exerted by a propeller engine or a jet engine with a view to slowing down the airplane and to reducing the braking distances upon a landing. On a jet engine, mobile members are moved so as to more or less completely obstruct the nozzle, thus deflecting forward the flow of hot gases from the turbine.

Thrust reverser deployment impacts on the aerodynamic flow around the static pressure probes and can result in a decrease of the static pressure being measured. Such a decrease of the static pressure leads to an increase of the displayed air speed, being calculated from such a measured static pressure.

Now, to avoid hot gases from being re-injected into the engines, thrust reversers are automatically deactivated beneath a given displayed air speed. Consequently, if the air speed is not optimally indicated, thrust reversers are not deactivated at the right time and the airplane can be submitted to hot gases being reinjected.

More precisely, upon the activation of the thrust reversers, an overpressure (or a depression) could occur being generated by hot air flowing on the static pressure probes, and involving a decrease (or an increase) of the CAS (<<Calibrated Airspeed>>) type corrected air speed. Thus:

-   -   in the case of a depression, the CAS corrected air speed is         overestimated and the thrust reversers are deactivated too late,         having thus as a direct effect hot gases being re-injected; and     -   in the case of an overpressure, the CAS corrected air speed is         underestimated and the thrust reversers are deactivated earlier         than necessary.

In both cases, braking or stopping thrust reversers is not optimized.

The present invention aims at solving the above mentioned drawbacks. It relates to a process for estimating an air speed of an airplane, being particularly accurate and not being disturbed, more specifically, by effects generated by the ground activation of the thrust reversers in the airplane.

To this end, according to this invention, said process wherein, automatically and repeatedly, the following operations are performed:

-   -   the static pressure and the total pressure are determined by         means of measurements performed by probes being on-board the         airplane; and     -   by means of said static pressure and said total pressure, an air         speed is calculated, representing the estimated air speed,         is remarkable in that, in addition, automatically, the following         operations are performed:     -   parameters of the airplane are monitored so as to be able to         detect a ground taxiing of said airplane; and     -   should a ground taxiing of the airplane be detected, the last         value of determined static pressure is registered, and a         correction is implemented, repeatedly performing the following         operations:         -   the total pressure is determined by means of measurements             performed by probes being on-board the airplane; and         -   by means of the thus determined total pressure and said             registered static pressure, an auxiliary air speed is             calculated representing the estimated air speed.

Thus, thanks to this invention, when the airplane is taxiing on the ground, after a rejected landing or takeoff, the static pressure is automatically frozen, being used for estimating the air speed so that the estimated air speed being obtained is not affected by the disturbances undergone by the static pressure probes on the ground, including further to the thrust reversers being activated.

Thus, on-board the airplane, an estimated air speed is available, in particular a CAS (<<Calibrated Airspeed>>) type corrected air speed or an IAS (<<Indicated Airspeed>>) type indicated air speed, being particularly accurate. Such an estimated air speed can be used by various systems of the airplane. In particular, it can be used for activating thrust reversers, as indicated therein below. In such a case, the above mentioned problems of reinjection of hot gases are avoided. Furthermore, braking is optimized, and no accelerated ageing occurs in the braking system of the airplane.

Moreover, advantageously, aground taxiing of the airplane is detected when at least one of the following conditions is met:

-   -   the landing gear of the airplane is in a compressed state;     -   the ground speed of the airplane is lower than a predetermined         speed value;     -   the airplane is in a ground phase; and     -   the static pressure is substantially equal to that corresponding         to the altitude of an airport used by the airplane.

Preferably, more particularly for detection reliability reasons, a ground taxiing of the airplane is detected when several of the previous conditions are simultaneously met.

Furthermore, advantageously, in order not to trigger the correction according to this invention in a flight phase or in another phase for which it is useless, said correction is not implemented when at least one of the following conditions is met:

-   -   the landing gear is in a decompressed state;     -   the ground speed of the airplane is larger than a predetermined         speed value;     -   the airplane is in a flight phase; and     -   the correction has already been implemented for a period of time         being larger than a predetermined period of time.

Furthermore, advantageously, in a particular embodiment, it could be contemplated to deactivate the implementation of previously activated correction, when at least one particular deactivation condition is met, for example, the ground speed of the airplane is larger than a predetermined speed value.

The air speed, being estimated according to this invention, could thus be used by various systems of the airplane so that several applications are possible.

In a preferred application, said estimated air speed of the airplane is used in a method for automatically managing the activation of thrust reversers in an airplane, wherein, when the thrust reversers are activated:

-   -   automatically and repeatedly, said estimated air speed is         compared to a predetermined speed value; and     -   as soon as said estimated air speed becomes lower than said         predetermined speed value, said thrust reversers are         automatically deactivated.

Thus, the estimated air speed to be used for deactivating thrust reversers is optimized so that the automatic deactivation is implemented at the appropriate time, i.e. neither too early nor too late. Thus, the above mentioned problems are overcome of hot gases being re-injected, which could occur in usual activations. Furthermore, braking is also optimized, and no accelerated ageing occurs in the braking system of the airplane.

Preferably, the thrust reversers are usually activated when usual activation conditions are met. However, in a particular embodiment, said thrust reversers are activated when the conditions relating to a ground taxiing, i.e. the above mentioned conditions intended for triggering the correction according to this invention, are met.

The present invention further relates to a device for automatically estimating an air speed of an airplane, in particular a transport airplane.

To this end, according to this invention, said device of the type comprising:

-   -   first means for repeatedly determining the static pressure and         the total pressure by means of measurements performed by probes         on-board the airplane; and     -   calculation means for repeatedly calculating, by means of said         static pressure and said total pressure, an air speed         representing the estimated air speed,         is remarkable in that it further comprises:     -   monitoring means for monitoring parameters of the airplane so as         to be able to detect a ground taxiing of said airplane;     -   registering means for registering, should a ground taxiing of         the airplane be detected, the last value of static pressure         determined by said first means; and     -   correction means for repeatedly calculating, should a ground         taxiing of the airplane be detected, by means of the total         pressure being the last determined by said first means and of         the static pressure registered by said registering means, an         auxiliary air speed representing the estimated air speed.

The present invention further relates to:

-   -   a system for managing the activation of thrust reversers of an         airplane, comprising a device such as specified herein above;         and/or     -   an aircraft, in particular a transport airplane, comprising such         a system or such a device.

The single FIGURE of the appended drawing will better explain how this invention can be implemented. Such a single FIGURE is the block diagram of a device according to this invention.

The device 1 according to this invention and schematically represented on the FIGURE is aimed at automatically estimating an air speed of an airplane (not shown), in particular a transport airplane, so as to provide an air speed being particularly accurate and not being disturbed, more specifically, by effects generated by the ground activation of thrust reversers in the airplane.

Said device 1 being on board is of the type comprising:

-   -   a set 2 of usual means M1, M2, . . . , Mn, n being an integer,         being on-board the airplane, for repeatedly measuring data         allowing to determine more specifically the static pressure and         the total pressure existing in the external environment of the         airplane. Said set 2 more specifically comprises total pressure         probes and static pressure probes; and     -   calculation means 3 being connected via a link 4 to said set 2         and being formed so as to repeatedly calculate, by means of said         static pressure and said total pressure, an air speed         representing the estimated air speed. Such an estimated air         speed could be supplied by means of a link 5 to user systems         (not shown) of the airplane and/or by means of a link 6 to means         7, to be specified herein below, for activating and deactivating         thrust reversers of the airplane.

Said static pressure and said total pressure could be calculated, by means of the data being measured, at the level of said set 2 or at the level of a unit 8 comprising said calculation means 3. Such a unit 8 could be an inertial reference and air data unit, including of the ADIRU (<<Air Data Reference Inertial Unit>>) type. Moreover, said set 2 could also comprise paddles or weathercocks for determining the leading and sideslip angles of the airplane, as well as total temperature probes.

The device 1 can perform, using more specifically calculation means 3, in particular the following operations:

A/ calculating the barometric altitude H as a function of the corrected static pressure P of the Mach effect and the leading edge. Calculating the barometric altitude H from the static pressure occurs by means of the following expressions:

${{- {if}}\mspace{14mu} \left( {P > {226.31881\mspace{14mu} {mb}}} \right)},{H = {{145447.2037\mspace{11mu} \left( {1 - \left( \frac{P}{1013.25} \right)^{0.1902545722}} \right)} - {{otherwise}\text{:}}}}$ $H = {36089.23885 + \left( {20805.85865\mspace{14mu} {\ln \left( \frac{226.31881}{P} \right)}} \right)}$

wherein:

-   -   H is the standard altitude; and     -   P is the corrected mean static pressure of the Mach effect and         the leading edge (conventional aerodynamic correction),

B/ calculating the corrected mean static pressure of the Mach effect and the leading edge (Ps=P), by means of the following expression:

Ps=Psi(1+G1+G2)

wherein G1 is a correction factor linked to the Mach, G2 a correction factor linked to the leading edge, and Psi the measurement of the static pressure indicated by the static pressure probe,

C/ calculating a dynamic impact pressure being defined by:

Qc=Pt−Ps

wherein Pt is the total pressure measured by the Pitot tube,

D/ calculating the CAS corrected air speed by means of the following expression:

${C\; A\; S} = {K\sqrt{\left( {\frac{Qc}{P_{0}} + 1} \right)^{\frac{2}{7}} - 1}}$

wherein K is a constant and P₀=1013.25 mbar,

E/ moreover, integrating different effects into the static pressure. A corrected static pressure of the ground effect could be calculated:

P{tilde under (s)}=Psi·(1+G1+G2+G _(ground) +G _(Train))

wherein G_(Ground) is a correction factor linked to the ground effect and G_(Gear) a correction factor linked to the effect of the landing gear,

F/ calculating the dynamic impact pressure being defined by:

Q{tilde over (c)}=Pt−P{tilde over (s)}

wherein Pt is the total pressure measured by the Pitot tube, and

G/ calculating the IAS indicated air speed by means of the following expression:

${I\; A\; S} = {K\sqrt{\left( {\frac{Q\overset{\sim}{c}}{P_{0}} + 1} \right)^{\frac{2}{7}} - 1}}$

wherein K is a constant and P₀=1013.25 mbar.

According to this invention, for determining an estimated air speed being particularly accurate and not being disturbed, including, by effects generated by the ground activation of thrust reversers in the airplane, said device 1 further comprises, as shown on FIGURE:

-   -   monitoring means 9, to be specified herein below, for monitoring         parameters of the airplane so as to be able to detect a ground         taxiing of said airplane;     -   registering means 10 for registering, on a usual registering         medium 11, should a ground taxiing of the airplane be detected,         the last value of static pressure determined by said means 2 or         8 and received by a link 12; and     -   correction means 13, being, for example, integrated into the         calculation means 3, for repeatedly calculating, should a ground         taxiing of the airplane be detected, by means of, on the one         hand, the total pressure being the last determined by said means         2 or 8 (and received by the link 12) and, on the other hand, of         the static pressure registered by said registering means 10 (and         received by a link 14), an auxiliary air speed that will be then         transmitted as an estimated air speed (via the links 5 and/or         6).

Such an air speed is calculated by means of the above mentioned calculations, but using, not the usual static pressure, but the static pressure registered by the means 10.

Thus, when the airplane is taxiing on the ground, after a rejected RTO (<<Rejected Take-Off>>) type landing or takeoff, the device 1 according to this invention automatically freezes the static pressure to be used for estimating the air speed so that the then obtained estimated air speed is not affected by the disturbances undergone by the ground static pressure probes, including further to the activation of thrust reversers.

An estimated air speed is thus available on-board the airplane, in particular a CAS (<<Calibrated Airspeed>>) type corrected air speed or an IAS (<<Indicated Airspeed>>) type indicated air speed being particularly accurate, whatever the phase of the airplane and including upon a ground taxiing of said airplane.

In a particular embodiment, said monitoring means 9 being connected via a link 16 to the unit 8 comprise monitoring members S1, S2, . . . , Sl, l being an integer, for monitoring parameters of the airplane, being representative of a ground taxiing of the airplane. Such monitoring members S1, S2, . . . , Sl could monitor, more specifically, parameters (compression state of the landing gear of the airplane, ground speed of the airplane, phase of the airplane, static pressure, etc.) allow to detect at least some of the following conditions:

-   -   the landing gear of the airplane is in a compressed state;     -   the ground speed of the airplane is lower than a predetermined         speed value;     -   the airplane is in a ground phase; and     -   the static pressure is substantially equal to that corresponding         to the altitude of an airport used by the airplane.

More specifically, for detection reliability reasons, the monitoring means 9, preferably, detect a ground taxiing of the airplane only when several of the previous conditions are simultaneously met.

Furthermore, in a particular embodiment, said device 1 comprises in addition means 17 for inhibiting the activation of the correction, so as not to trigger the correction according to this invention in a flight phase or in another phase for which it is useless. Using such means 17 being connected by means of a link 18 to the unit 8, the device 1 does not implement said correction when one or more of the following conditions are met:

-   -   the landing gear is in a decompressed state;     -   the ground speed of the airplane is larger than a predetermined         speed value;     -   the airplane is in a flight phase; and     -   the correction has already been implemented for a period of time         being larger than a predetermined period of time, for example,         one minute.

Moreover, in a particular embodiment, said device 1 further comprises means 19 being connected via a link 20 to the unit 8 and being formed so as to deactivate the implementation of a previously activated correction, when at least one particular deactivation condition is met, for example, when the ground speed of the airplane is larger than a predetermined speed value.

The air speed, being estimated according to this invention, could be used by various systems of the airplane so that several applications are possible.

In a preferred application, the device 1 is part of a system 21 for automatically managing the activation of usual thrust reversers (not shown) of the airplane. Such a system 21 comprises, in addition to the device 1, said means 7 for activating and deactivating thrust reversers, controlling the thrust reversers via a link 22. Such means 7 comprise means 23 for usually activating said thrust reversers when usual activation conditions (received by a link 24) are met.

Said means 7 further comprise means 25:

-   -   for comparing, automatically and repeatedly, said estimated air         speed received from the device 1 via the link 6 to a         predetermined speed value; and     -   for automatically deactivating said thrust reversers(via the         link 22) as soon as said estimated air speed becomes lower than         said predetermined speed value.

Thus, the estimated air speed to be used for deactivating thrust reversers is optimized so that the automatic deactivation is implemented at the appropriate time, i.e. neither too early nor too late. As a result, the above problems of hot gases being re-injected that could occur with the usual activations are avoided. Furthermore, braking is also optimized, and no accelerated ageing occurs in the braking system of the airplane.

In a particular embodiment, said means 23 are linked by the link 24 to said monitoring means 9 and they activate said thrust reversers when the conditions relating to a ground taxiing, i.e. the above mentioned conditions intended for triggering the correction according to this invention, are met. Thus, in this particular embodiment, the monitoring means 9 allow to both trigger the correction implemented by the device 1 and the activation of thrust reversers. 

1. A process for automatically estimating an air speed of an airplane, said process wherein, automatically and repeatedly, the following operations are performed: the static pressure and the total pressure are determined by means of measurements performed by probes being on-board the airplane; and by means of said static pressure and said total pressure, an air speed is calculated, representing the estimated air speed, is characterized in that, in addition, automatically, the following operations are performed: parameters of the airplane are monitored so as to be able to detect a ground taxiing of said airplane; and should a ground taxiing of the airplane be detected, the last value of determined static pressure is registered, and a correction is implemented, repeatedly performing the following operations: the total pressure is determined by means of measurements performed by probes being on-board the airplane; and by means of the thus determined total pressure and said registered static pressure, an auxiliary air speed is calculated representing the estimated air speed.
 2. The process according to claim 1, characterized in that a ground taxiing of the airplane is detected when at least one of the following conditions is met: the landing gear of the airplane is in a compressed state; the ground speed of the airplane is lower than a predetermined speed value; the airplane is in a ground phase; and the static pressure is substantially equal to that corresponding to the altitude of an airport used by the airplane.
 3. The process according to claim 1, characterized in that said air speed is a corrected air speed.
 4. The process according to claim 1, characterized in that said air speed is an indicated air speed.
 5. The process according to claim 1, characterized in that said correction is not implemented when at least one of the following conditions is met: the landing gear is in a decompressed state; the ground speed of the airplane is larger than a predetermined speed value; the airplane is in a flight phase; and the correction has already been implemented for a period of time being larger than a predetermined period of time.
 6. The process according to claim 1, characterized in that the implementation of the correction is deactivated when at least one deactivation condition is met.
 7. A method for automatically managing the activation of thrust reversers in an airplane, said method wherein, when the thrust reversers are activated: automatically and repeatedly, an air speed of the airplane is estimated, and compared to a predetermined speed value; and as soon as said estimated air speed becomes lower than said predetermined speed value, said thrust reversers are automatically deactivated, characterised in that said air speed of the airplane is estimated, implementing the process specified in claim
 1. 8. The method according to claim 7, characterized in that said thrust reversers are activated when the conditions relating to a ground taxiing are met.
 9. A device for automatically estimating an air speed of an airplane, said device comprising: first means (2) for repeatedly determining the static pressure and the total pressure by means of measurements performed by probes on-board the airplane; and calculation means (3) for repeatedly calculating, by means of said static pressure and said total pressure, an air speed representing the estimated air speed, characterized in that it further comprises: monitoring means (9) for monitoring parameters of the airplane so as to be able to detect a ground taxiing of said airplane; registering means (10) for registering, should a ground taxiing of the airplane be detected, the last value of static pressure determined by said first means (2); and correction means (13) for repeatedly calculating, should a ground taxiing of the airplane be detected, by means of the total pressure being the last determined by said first means (2) and of the static pressure registered by said registering means (10), an auxiliary air speed representing the estimated air speed.
 10. A system for automatically managing the activation of thrust reversers in an airplane, said system (21) comprising; calculation means for, automatically and repeatedly, estimating an air speed of the airplane, and comparing it to a predetermined speed value; and deactivation means (25) for automatically deactivating said preliminarily activated thrust reversers, as soon as said estimated air speed becomes lower than said predetermined speed value, characterized in that said calculation means comprise a device (1) such as specified in claim 9, for automatically estimating the air speed of the airplane. 